This disclosure relates to the conversion of heat energy to mechanical energy. The disclosure further relates to such conversion where the heat energy source is concentrated solar energy.
Several different types of heat engines have been used in practice to convert concentrated solar radiation to mechanical power, notably Stirling cycle engines and Rankine cycle engines, however, all such known engines have had disadvantages relating to complexity, cost or low efficiency. Apparatus which convert heat energy into mechanical energy, namely the heat energy of concentrated beam of solar radiation into the movement of a piston through the explosion or expansion of a droplet of substantially uncompressed liquid targeted by the concentrated solar beam are described in patent application Ser. No. 11/512,568, referred to above. In patent application Ser. No. 11/512,568, a method of utilizing a droplet or thin film of water or other liquid, which is heated and explosively expanded in a six-sided expander, is described. The six-sided expander absorbs substantially all of the energy in the droplet and converts a large fraction of that energy to mechanical power through the motion of a linear piston. Mechanical power is in turn converted to electrical power by a linear generator on each of the six sides complete with field excitation and output coil.
In theoretical, conventional Rankine cycles, expansion of working fluid takes place under reversible adiabatic conditions. Also in conventional Rankine cycles as applied to solar energy conversion, the fluid is first vaporized in a boiler then passed into an expander.
Methods whereby liquid is injected into a working space above a piston have also been described. Conventionally, the hot liquid vaporizes at the point of injection, with consequent loss of available energy or exergy. Some of the initial energy loss on vaporization of liquid injected into the cylinder may be regained as heat transferred from the compressed vapor already within the cylinder; however, the energy thus transferred comprises no net heat addition from outside but merely constitutes energy re-circulated within the system. Such recirculation cannot, of itself, produce a useful energy output by the system.
Thus, in the liquid injection prior art, fluid is injected, with exergy loss into a chamber, during which relatively uncontrolled vaporization takes place reducing the amount of available energy, then work is done by adding heat back into the already partially expanded vapor to cause the further expansion of the vapor which moves a piston to perform useful work.